Recent studies have established a genetic linkage of cyld to both familial and sporadic neoplasms that mostly arise from the epidermal cells of skin appendages, as distinct from surface epidermal cells. CYLD acts as a deubiquitinase that inhibits self-ubiquitination of TRAF2/TRAF6 proteins, the key adaptor molecules mediating signal transduction from cell surface receptors, and thereby inhibit downstream signaling pathways, including NF-?B and JNK signaling cascades. A previously predicted role for the canonical NF-?B pathway in the etiology of skin neoplasms was recently challenged by findings revealing unaltered NF-KB RelA function in the TPA-induced hyperproliferation of cyld-/- mice epidermal cells. In addition, we have recently demonstrated that NF-?B is crucial in epidermal growth control and its blockade contributes to squamous cell carcinoma (SCC) in a JNK/AP1 function dependent manner. These finding lead us to hypothesize that CYLD inhibition acts through JNK cascade to promote neoplasia. The first goal of this study is to define the mechanisms of CYLD regulation of epidermal cell growth and to explore whether the JNK signaling cascade play a central role in CYLD effects on epidermal homeostasis. To do this, we will isolate multiple types of primary human epidermal cells from surgically disposed foreskin or adult skin and study their growth response to genetically modified CYLD function, as well as JNK signaling. The second goal is to study CYLD-driven neoplasia in vivo by generating both mice and human transgenic skin tissue. We will investigate whether inhibiting or augmenting NF-?B, JNK or Ras-MAPK signaling cascades will prevent or potentiate CYLD induced neoplasia. By the end of this proposal, we hope to have determined the mechanism of CYLD regulation of epidermal homeostasis and cutaneous epithelial neoplasms. This effort is based on the premise that characterizing the molecular mechanisms in CYLDmediated cell growth and neoplasia in skin tissue will both provide new insights into basic epithelial biology as well as characterize therapeutic targets for human skin diseases.